This application claims Paris Convention priority of German patent application 198 59 434.8 filed Dec. 22, 1998, the complete disclosure of which is hereby incorporated by reference.
The invention concerns a device for the optical-spectroscopic examination of interior surfaces of a body, e.g. of blood vessels, comprising an optical spectrometer and an endoscope with a light guiding means for the illumination of surfaces, wherein light is guided into the light guiding means at its proximal end and at its distal end the light is launched at the surfaces to be examined, wherein the distal end of the endoscope comprises a means for receiving the light reflected by the surfaces to be examined.
A device of this type is known in connection with an infrared (=IR) spectrometer from DE 197 32 215 A1, wherein reference is made to the said complete document.
With endoscopes of this type, scattered light is guided from interior surfaces of a body, mainly from blood vessels or cavities inside the body, via light guides to an external detector to the outside. Usually glass fiber bundles are used as light guides. As an alternative, also NIR transparent materials like silver hologenides or chalcogenides can be used. The intensity of the scattered light received and thus the signal intensity of the signal received is mainly proportional to the product of the cross-sections of the fibers, which guide the light from the spectrometer through the endoscope for recording, and of the cross sections of those fibers would receive the scattered light and guided outside to the detector.
A disadvantage of an endoscope of this type consists in that on the one hand the light directed to the surfaces to be examined, if. e.g. the inner vascular walls in a human body are to be examined, has to pass at first from the distal end of the light guiding means through the blood or other body fluids to the surface to be examined, and that the light reflected or scattered from there, has to penetrate the corresponding fluid again on its way back to the endoscope, said fluid normally being in motion, such that the local density may change with time. A further disadvantage consists also in that the distal end of the endoscope is not fixed, and thus shaking and a change of relative distances may happen during measurements, thus reducing the quality of the recorded optical spectra.
In contrast thereto, it is the object of the present invention to improve a device of the initially defined type in as simple as possible manner to obviate the above-mentioned disadvantages.
According to the invention, this object is achieved in a both simple and effective manner in that the distal end of the light guiding means is arranged within an inflatable balloon with an elastic exterior and that the light launched at the light guiding means and also the light reflected from the surfaces to be examined to the recording device penetrates in each case the exterior of the balloon.
Inflation of the balloon at the distal end of the light guiding means causes displacement of body fluids and of flowing blood and the exterior of the balloon abuts in a fixing manner in the area of the vascular inner wall to be examined such that the distal end of the endoscope does no longer change its relative distance from the surrounding wall of the vessel in the inflated state of the balloon. Thus, outer influences that change with time and might have a disadvantageous effect on the quality of the spectra are eliminated.
Inflatable balloon catheters as such are known in general, e.g. from xe2x80x9cPschyrembel Klinisches Wxc3x6rterbuchxe2x80x9d, Walter de Gruyter-Verlag, Berlin, N.Y., 1986, pages 170, 531, 622 and 1536. These known balloon catheters are, however, not used in connection with optical spectrometers. Their mechanical and optical construction is thus not suited to be used with a device according to the present invention.
One embodiment of the inventive device is preferred, wherein the elastic exterior comprises transparent sections in the area where the light enters and exits. In this way it is possible to optimize the elastic properties of the exterior of the balloon on the one hand and their optical properties in the area of the interesting surfaces on the other hand, independently of one another.
It is e.g. feasible to insert transparent xe2x80x9cwindowsxe2x80x9d in the corresponding sections of the exterior of the balloon. However, one embodiment is preferred in which the material of the elastic exterior is selected such that it is largely transparent in the spectral range of interest. In this manner, the light used for the spectroscopic examination may theoretically penetrate the exterior of the balloon unhindered at any point and it is not required to insert transparent sections under great efforts, but the exterior of the balloon can be produced of one piece.
In further embodiments of the invention, the elastic exterior of the balloon may preferably be formed of latex material which is known to be medically well compatible, has been tested for decades and is readily available. At least if the thickness of the exterior of the balloon is small, it is possible to achieve sufficient transparency in a large wave-length range.
In a particularly preferred manner, the balloon can be inflated with inert gas, preferably with helium. The path of rays in the direction of the surfaces to be examined and also away from the surfaces towards the detector extends in a chemically inert, optically highly transparent homogeneous medium.
In a particularly preferred embodiment of the device according to the invention, the elastic exterior of the balloon is constructed in such a manner that, in its inflated state, a cross-section of passage of a blood vessel to be examined remains open. In this manner, the passage of blood during vascular examinations can be maintained at least to a limited degree which may be vital with certain blood vessels.
In an advantageous further development of this embodiment, the exterior of the inflated balloon has at least one radial recess in its cross-section along the entire axial extent of the balloon which produces a cross-section of passage outside of the exterior of the balloon.
This further development is particularly easy to realize in that the exterior of the balloon in the area of the recess is formed of a thicker, reinforced and/or stiffened material. When the balloon is inflated, the exterior in this area will remain essentially rigid such that the desired recess will be formed there.
In an alternative further development, a continuous hollow channel extends along the axis of the endoscope through the elastic exterior of the balloon thus maintaining a defined and constant cross-section of passage through the balloon.
This is achieved in a particularly preferred manner by disposing the hollow channel on the axis of the endoscope and arranging the elements of the light guiding means, in particular optical fibers, in a circle around the hollow channel. This geometrical arrangement does not restrict the field of view of the endoscope. Despite the hollow channel it is possible to examine 360xc2x0 of the surrounding surfaces in an annular view.
One embodiment of the device according to the invention is also advantageous in which the distal end of the light guiding means can be displaced relative to the exterior of the balloon, preferably in the direction of the longitudinal axis of the endoscope.
With a stationary endoscope, it is still possible to obtain recordings with longitudinal local dependency.
In a particularly preferred embodiment, the illuminated distal end of the light guiding means is provided with an ultrasound head which is rotatable preferably about the longitudinal axis of the endoscope. In this manner, critical locations, e.g. vascular constrictions can be pre-localized through ultra sound images and can subsequently be examined by an infrared spectroscope which images may serve e.g. for identifying the type of tissue or for analyzing depositions.
The light guiding means in embodiments of the invention may comprise one or more fiber bundles which have been available on the market for many years.
In a preferred further development of these embodiments, the distal end of the light guiding means is provided with means for deflecting the light by approximately 90xc2x0. In this way it is possible to illuminate an area to be examined which is transverse to the longitudinal axis of the endoscope as it is typically the case with blood vessels.
The deflection may be effected via a preset mirror or via a prism disposed onto the fiber bundle.
In a further development which is particularly easy to produce and thus cheap, the fiber ends themselves are chamferred altogether in the form of a prism at an angle of approximately 45xc2x0. The deflection of the light is effected by total reflection or by disposing mirrors on the chamferred surface.
In embodiments, the spaces between the fibers of the fiber bundle in the area where the light exits are filled with a material which has a refractive index in the IR spectral range of interest such that the refractive index difference between the fiber and material is small enough to transmit the IR light which comes in at an almost perpendicular angle and is reflected from the chamferred fiber ends.
In this manner, the light bundles emitted by a central fiber may penetrate the edge fibers largely without any loss of reflection.
To ensure the guidance of the IR light in the fibers, the fiber surfaces outside of the area where the light exits, may be lined with mirrors.
A particularly easy further development of the invention is characterized in that the means for deflecting the IR light are formed by abrading the ends of the optical fibers in a plane manner perpendicularly to the longitudinal axis of the endoscope, and by arranging mirrors in an axial direction behind the optical fiber ends at the distal end of the endoscope.
In this connection, the mirror arrangement may comprise a parabolic mirror which enables the generation of a parallel beam.
The mirror arrangement may also comprise an elliptical mirror, whereby the ends of the light guiding means where the light exits, can be reproduced in a focussing manner.
One variant is particularly easy in which the mirror arrangement comprises a plane mirror such that a simple non-reproducing deflection of the beams is effected.
In embodiments of the inventive device, the light guiding means may supply light for irradiating the surface to be examined as well as return light received from the surface to a detector as it is the case with most endoscopic arrangements.
A further development of this embodiment is characterized in that the fiber bundles are formed, in each case, of a central afferent fiber which guides light in the direction towards the surface to be examined, and of several efferent fibers which are arranged in circles around the central fiber and return light from the surface to the detector. In this manner, the useful cross-section of the endoscope is utilized to an optimum degree.
One variant of this embodiment is of particular advantage in which the fiber bundles are arranged on the inside of a surrounding exterior in the form of a circle.
The spectrometer may also be a Raman spectrometer. Illumination of the surfaces to be examined is effected by monochromatic light of high intensity. The Raman effect measured offers information which is complementary to the usual absorption or reflection spectrometry. Furthermore, it can be used to observe information from a totally different spectral range.
Embodiments of the device according to the invention are particularly preferred in which the optical spectrometer is an infrared (=IR), in particular a near infrared (=NIR) spectrometer. Infrared spectrometry is probably one of the main applications of optical endoscopes of this type in the medical field. For this purpose, glass fibers for the light guiding means which are optimized in the infrared wavelength range are available in a wide variety.
One further development of this embodiment is preferred, wherein the IR spectrometer is a Fourier spectrometer with an interferometer which converts the signals coming from the surface to be examined into an interferogram and by means of Fourier transformation into an IR spectrum. In this way, it is possible to achieve shorter measuring times and improved light intensities.
In a further development, the light guided into the light guiding means at the proximal end of the endoscope is launched by the IR spectrometer. This allows particularly easy connection of the endoscope to commercial IR spectrometers.
One further development is particularly preferred, wherein the distal end of the light guiding means comprises a detector for receiving and converting IR light scattered on the illuminated surface, into electric signals. An arrangement of this type is known from the initially cited DE 197 32 215 A1 to the full contents of which is referred to again and the further developments of which can be combined without any problems with the basic idea of the present invention. This arrangement, which is known per se, in connection with the device according to the invention improves the signal strength and thus additionally enables reduction of the measuring time thus maintaining the same signal quality.
In a preferred further development, the light-sensitive surface of the detector is mounted directly on an outer surface of the light guiding means. In this manner, the detector does practically not require additional space and the endoscope of the inventive device can be constructed in a particularly compact manner.
One embodiment is particularly preferred in which the distal ends of the fibers of the fiber bundle are arranged in a circle on the inner wall of a detector which is also of annular shape.
This arrangement itself without the features of the inventive device mentioned above, offers great advantages in itself, and particularly high light penetration through the endoscope. The exiting light does not have to penetrate any filling material or other fibers of the light guiding means. In this manner it is possible to avoid complicated geometrical configurations of the light guiding fibers.
In a particularly preferred variant of the inventive device, the sensitive surface of the detector in the peripheral direction of the endoscope is constructed in lateral segments. This enables locally-resolved measurements without any problems if the signals from the individual detector segments are processed separately.
In this connection, it is again particularly advantageous to associate each detector segment with at least one unique fiber illuminating the surface to be examined.
In another further development, which can be realized in a particularly advantageous manner in combination with the above further development, each fiber is supplied with light separately. In this manner, it is possible to produce an information matrix from the signals of the surfaces to be examined which enables a considerably better local resolution.
A method of operating a device of the above-mentioned type lies also within the scope of the present invention in which the fibers are supplied with light in the time multiplex to obtain a corresponding locally-resolved spectrum.
As an alternative or supplement, in a further variant of the method the signals received in the detector segments can be read out in the time multiplex. In this way it is possible to achieve an even better local resolution of the spectra.
Further advantages of the invention can be gathered from the description and the drawing. The features mentioned above and below may be used according to the invention individually or collectively in any arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but rather have exemplary character for describing the invention.